Method and system for multicasting over a UTOPIA bus

ABSTRACT

According to one embodiment of the invention, a method for multicasting data includes receiving, at a line card multicast data and an indication of a plurality of destinations for the multicast data. The method also includes transferring the multicast data over a common bus to a plurality of digital subscriber line chipsets associated with the plurality of destinations. Such transfer occurs by selecting two or more of the plurality of digital subscriber line chipsets to receive multicast data, enabling the two or more selected digital subscriber line chipsets to receive the multicast data, and transferring the multicast data over the common bus to the selected digital subscriber line chipsets after selection and enabling of the two or more of the plurality of digital subscriber line chipsets.

TECHNICAL FIELD OF THE INVENTION

This invention relates generally to telecommunications and moreparticularly to a method and system for multicasting over a UTOPIA bus.

BACKGROUND OF THE INVENTION

Data communications is becoming increasing important in today's society.Many media exist for transmitting data, including the airways, cable,and telephone lines. As technology develops, these types of media may beused in new ways. For example, video data, such as television, hastraditionally been transmitted over either cable or the airways.However, technology enhancements may allow such transmissions to occurin a viable fashion over telephone lines. One problem associated withtransmitting video or other types of data over telephone lines isaddressing how to transmit data to multiple locations, referred toherein as multicasting.

One format for communicating data is asynchronous transfer mode (ATM)format. Many other formats exist. According to one technique, an ATMswitch addresses multicasting by identifying a data cell as a multicastcell and then making multiples copies of the cell. The multiple copiesare stored in memory and transmitted separately at an appropriate timeto each destination. A problem with this approach is that transmittingmultiple copies of data is time-consuming and contributes to switchlatency.

SUMMARY OF THE INVENTION

According to one embodiment of the invention, a method for multicastingdata includes receiving, at a line card multicast data and an indicationof a plurality of destinations for the multicast data. The method alsoincludes transferring the multicast data over a common bus to aplurality of digital subscriber line chipsets associated with theplurality of destinations. Such transfer occurs by selecting two or moreof the plurality of digital subscriber line chipsets to receivemulticast data, enabling the two or more selected digital subscriberline chipsets to receive the multicast data, and transferring themulticast data over the common bus to the selected digital subscriberline chipsets after selection and enabling of the two or more of theplurality of digital subscriber line chipsets.

According to another embodiment of the invention, an apparatus comprisesa buffer, a plurality of UTOPIA physical devices each coupled to acommon bus, and a plurality of polling units. Each polling unit isoperable to poll at least a respective one of the UTOPIA physicaldevices to determine if at least one respective UTOPIA physical deviceis ready to receive data. The apparatus also includes a select unit. Theselect unit is operable to receive an indication from each of theplurality of polling units that a respective UTOPIA physical device isready to receive data. The select unit is also operable to initiateenabling of selected ones of the physical devices that are ready toreceive data and for which any data stored in the buffer is intendedsuch that more than one of the UTOPIA physical devices are able toreceive data at the same time. The select unit is further operable toinitiate transfer of data stored in the buffer over a common bus toenable the UTOPIA physical device. The apparatus also includes atransfer unit operable to transmit the data stored in the buffersimultaneously to the enabled UTOPIA physical devices.

Some embodiments of the invention provide numerous technical advantages.Other embodiments may realize some, none, or all of these advantages.For example, according to one embodiment, a plurality of physicaldevices may receive data at the same time through one transfer of data.This contrasts with previous systems in which multicast data must betransmitted multiple times for each recipient. By allowing multiplerecipients to receive the same transfer data, the bandwidth of anassociated line card may be increased. Increasing the bandwidth allowsthe line card to accommodate more data requests and more customers.

Other technical advantages may be readily ascertainable by one of skillin the art.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference is now made to the following description taken in conjunctionwith the accompanying drawings, wherein like reference numbers representlike parts, in which:

FIG. 1A is a schematic diagram of a telecommunications system accordingto the teachings of the invention;

FIG. 1B is a block diagram showing additional details of the line cardof FIG. 1A;

FIG. 2 is a block diagram showing additional details of the ATM UTOPIAmaster controller of FIG. 1B;

FIG. 3 is a state diagram of the select unit of FIG. 2;

FIG. 4 is a state diagram of the polling unit of FIG. 2;

FIG. 5 is a state diagram of the transfer unit of FIG. 2; and

FIG. 6 is a block diagram of an alternative embodiment of the UTOPIAmaster controller of FIG. 2.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the invention are best understood by referring to FIGS. 1through 6 of the drawings, like numerals being used for like andcorresponding parts of the various drawings.

FIG. 1A is a block diagram of a telecommunications system 10 accordingto the teachings of the inventions. Telecommunications system 10includes a plurality of homes or businesses (or other locations) 12(referred to herein as “customer premises 12”) and a network 14, such asan Internet protocol network. A central office 16 receives a pluralityof telephone lines 24 coupled to respective ones of customer premises12. Network 14 couples to central office 16 through a trunk line 34.Trunk line 34 may be any suitable communication link that may carryInternet protocol traffic, including OC3, DS3, T1 (STM1, E3, E1, in.Europe).

Central office 16 comprises, among other components not explicitlyshown, a digital subscriber line access multiplex or DSLAM 18. DSLAM 18comprises, in this example, a first network interface card 20, a secondnetwork interface card 22, and a plurality of line cards 26. DSLAM 18generally allows communication between customer premises 12 and network14. Network interface card 20 communicates with network 14 over line 34(connection not explicitly shown in FIG. 1). Network interface card 20receives data from network 14 over line 34 and communicates it to aparticular line card 26 associated with the intended destination of thedata. Conversely, network interface card 20 receives data form linecards 26 and communicates it over line 34 to network 14. Networkinterface card 20 also contains the IP/ATM switch fabric that managesand processes packets and cells. It manages all aspects of the DSLAM 18,including system help, system performance, switch help and performance,and network communications. Network interface card 22 may serve as abackup for network interface card 20. In some embodiments, networkinterface card 22 is omitted.

Line cards 26 receive communications over telephone lines 24 (connectionnot explicitly shown in FIG. 1A) from a customer premises 12 andcommunicate that information to network interface card 20 for eventualtransmission to network 14. Conversely, line cards 26 receivecommunications through network interface card 20 from network 14 andcommunicate it to a particular one of customer premises 12 over line 24.Line cards 26 are described in greater detail below in conjunction withFIG. 1B.

FIG. 1B is a block diagram showing portions of line card 26 and networkinterface card 20 of FIG. 1A. As illustrated, line card 26 is coupled tonetwork interface card 20 by a communication link 36. Communication link36 may be a UTOPIA bus connected across a backplane of DSLAM 18, in oneembodiment; however, communication link 36 may take other forms. Linecard 26 includes an ATM UTOPIA master controller 28 coupled to aplurality of DSL chipsets, or modems 30, by a UTOPIA bus 32. DSLchipsets 30 provide received data to an associated customer premises 12over telephone line 24. Network interface 20 couples to network 14through trunk line 34. A plurality of buses 37 such as high speed serialbuses may couple the other line cards 26 to network interface card 20(not explicitly shown in FIG. 1B). ATM UTOPIA master controller 28controls transfer of data received from network interface card 20 overline 36 through the various DSL chipsets 30. Data may be transferredfrom ATM UTOPIA master controller 28 to DSL chipsets 30 over a data bus56 (shown in FIG. 2). Additional details of ATM UTOPIA master controller28 are described with respect to FIG. 2 below. ATM UTOPIA mastercontroller 28 may be implemented as a field programmable gate array(FPGA), as an application specific integrated circuit (ASIC), or may beimplemented in other suitable forms. DSL chipsets 30 are UTOPIA physicaldevices, sometimes referred to as PHY's. Each DSL chipset 30 operates asa slave of ATM UTOPIA master controller through UTOPIA bus 32.

Conventionally, an ATM UTOPIA master controller addresses multicast dataas follows. A polling engine within the master controller polls aphysical device, such as DSL chipset 30, by placing the physicaldevice's address on bus 32. When the DSL chipset 30 sees its own addresson UTOPIA bus 32, it places a cell available signal on the bus forreceipt by the polling engine. In response, the polling engine placesthe same address again on UTOPIA bus 32, indicating that the addressedDSL chipset is selected to receive data. In response to selecting aparticular DSL chipset to receive data, data that has been received fromnetwork interface card 20 is transferred to the selected device over adata bus. This procedure is repeated for each recipient of the multicastdata. Thus, if four customer premises associated with respective ones ofDSL chipsets 30 each wish to receive the multicast data, four separatepolling, selection, and transfer of data steps are applied.

According to the teachings of the invention, rather than polling each ofDSL chipsets 30 with a single polling controller, and thus requiring aseparate transfer of data for each recipient, either a separate pollingengine is provided for each DSL chipset, or a separate polling engine isprovided for a group of DSL chipsets 30. By allowing separate polling ofvarious DSL chipsets, multicast data may be transferred to more than oneDSL chipset at any given time, reducing the number of transfers thatneed to take place to distribute multicast data to all intendedrecipients. By being able to transfer multicast data to more than oneDSL chipset at the same time, the bandwidth available from line card 26is increased. Details of one embodiment of the invention are describedin greater detail with respect to FIGS. 2 through 5, and details of analternative embodiment are described with respect to FIG. 6.

FIG. 2 is a block diagram showing additional details one embodiment ofline card 26 according to the teachings of the invention. Line card 26includes a random access memory (RAM) 38, a select unit 40, a pluralityof polling units 42, a transfer unit 54, and a plurality of DSL chipsets30, in this embodiment. Random access memory 38 comprises any suitableform of memory for storing data for receipt by DSL chipsets 30. Selectunit 40 controls selection of which ones of DSL chipsets 30 to select toreceive data, as described in greater detail below in conjunction withFIG. 3. Polling units 42 poll, in this example, an associated one of DSLchipsets 30 to determine if the DSL chipset is ready to receive data.According to the teachings of the invention, a separate polling unit isprovided for each DSL chipset 30, in this embodiment.

Transfer unit 54 receives instructions from select unit 40 over line 41instructing transfer unit to transfer data stored in random accessmemory 38 onto a data bus 56. Data bus 56 may be any suitable link forproviding data to one or more UTOPIA devices, such as DSL chipsets 30.In this example, data bus 56 is a 16 bit data bus with a start of cell(SOC); however, other sizes of data buses may be used. Each polling unit42 is coupled to select unit 40 by a select line 46 and a cell availableline 48. Each polling unit 42 is also coupled to a DSL chipset 30 by anaddress line 50 and a cell available line 52. In this example, lines 46,48 and 52 are all one bit lines; however, other suitable sizes of linesmay be used. Address line 50 may be any suitable size; however, forUTOPIA 2 communications, a five-bit address line is used in oneembodiment. For UTOPIA 3 communication, lines 50 having greater thanfive bits of bandwidth are particularly advantageous.

In operation, each polling unit 42 places the address of its associatedDSL chipset 30 on its associated address line 50. The polling unit 42then idles when it receives a cell available signal from the DSL chipset30 over line 52. The receipt of the cell available signal over line 52indicates that the associated DSL chipset 30 is ready to receive data.In response to polling unit 42 receiving a cell available signal overline 52, polling unit 42 transmits a cell available signal over line 48to select unit 40 identifying the associated physical device that isready prepared to receive data.

Select unit 40 examines data received in random access memory 38 todetermine its destination. In one example, the data stored in randomaccess memory comprises a cell of data having an associated fieldidentifying the destination address or addresses. In response toreceiving cell available signals from polling units 42 identifying DSLchipsets 30 that are ready to receive data and select unit identifyingthese DSL chipsets 30 as ones for which the multicast data are intended,select unit 40 selects those DSL chipsets and directs transfer unit 54,over line 41, to initiate transfer of the data out of random accessmemory 38 onto data bus 56. Such initiation of transfer may occurimmediately upon identifying a particular one of DSL chipset 30 that isprepared to receive data, or may take place after identification of aplurality of such DSL chipsets 30. In one embodiment, all DSL chipsets30 for which data are intended are enabled before data are transferred.In another embodiment, only some DSL chipsets 30 are enabled at the sametime and multiple transmissions of the same data are required.

Select unit 40 selects a DSL chipset to receive data by directing theassociated polling unit, over line 46, to select the DSL chipset. Thepolling unit 42 selects the DSL chipset by again placing the address ofthe physical device on address line 50. According to UTOPIA protocol,upon again receiving its address on address line 50, the DSL chipset 30enables itself to read data on data bus 56. This selection procedure maytake place for each DSL chipset 30 identified as an intended address forthe data in random access memory 38. Thus, for multicast data, aplurality of DSL chipsets 30 may be selected to receive data residing ondata bus 56 at substantially the same time. In contrast, in conventionalsystems utilizing only one polling unit, only one DSL chipset could beselected at a time. This means that multicast data must bere-transferred from random access memory 38 to the DSL chipsets for eachintended address, which causes undue delay.

With respect to multicast data, line card 30 provides greater bandwidththan some other line cards that do not utilize more than one pollingunit. The provision of more than one polling unit 42 allows multiple DSLchipsets 30 to receive data transmitted over data bus 56 atsubstantially the same time. Polling unit 42 and DSL chipset 30 may beformed according to conventional techniques and may be the same type ofpolling unit and physical device utilized in line cards having only onepolling unit.

Thus, a system and method are provided that allow multicasting of datain a reduced number of data transfer procedures, rather thantransmitting the same data once for each and every destination. Such amethod increases bandwidth on data bus 56, in one example, and reducesthe overall bandwidth required for multicasting. Additional detailsregarding select unit 40, polling units 42, and transfer unit 54 aredescribed with respect to FIGS. 3 through 5.

FIG. 3 is a state diagram of select unit 40. At step 60, select unit 40waits until data are ready to be transferred from random access memory38. In this example, data are stored in cells; however, any suitablegrouping of data may be used. In addition, select unit 40 waits until acell available status signal is received over one of cell availablelines 48, as indicated by reference numeral 58. Such a cell availablesignal is received from a polling unit 42, which continually monitorsits associated DSL chipset for a cell available signal received overline 52. This monitoring is performed at step 66. If a cell is ready fortransfer from random access memory 38 and a cell available signal isreceived by select unit 40, select unit 40 directs the associatedpolling engines from which cell available signals were received toselect the associated DSL chipset 30 to receive data. Polling units 42may select the DSL chipset 30 by outputting, on its associated addressline 50, the address of the DSL chipset 30. At step 64, select unit 40instructs transfer unit 54 to read the data from random access memory 38and send it across UTOPIA bus 56 for receipt by the appropriate physicaldevices 30. Step 64 may occur at any suitable time, such as a time afterwhich a certain number or percentage of the DSL chipsets intended toreceive multicast data are selected.

FIG. 4 is a state diagram of polling units 42. At step 70, polling unit42 places the address of its associated physical device on address line50. At step 72, polling unit 42 idles and continues to poll until itreceives a cell available signal from its associated physical device atstep 74. In response to receiving a cell available signal at step 76,polling unit 42 informs select controller 40 that its associatedphysical device 30 is available to receive data by providing a cellavailable signal over line 48. As described above, after instructed todo so by select unit 40, polling unit 42 also places the address of theassociated DSL chipset 30 on the address line 50 again to select the DSLchipset 30 to receive data.

FIG. 5 is a state diagram of transfer unit 54. At step 78, transfer unitaccesses random access memory 38 and begins the transfer process oftransferring data stored within the memory to bus 56. This process isinitiated by a signal received from select unit 40 over line 41, asdenoted by reference numeral 77. At step 80, the RAM address identifyingthe location of data to be transferred is incremented and provided torandom access memory 38. At step 82, data are received by transfer units54 from random access memory 38. At step 84, transfer unit 54 places astart of cell (SOC) signal and a cell enable signal on data bus 56 toidentify for the selected DSL chipsets 30 that data are about to betransferred to them. At step 86, transfer unit 54 transmits the dataread from random access memory 38 onto data bus 56. Processing continuesat step 80 until all data designed for the selected DSL chipsets 30 havebeen transmitted to data bus 56, except that at step 84 sending a startof cell (SOC) signal occurs only once before any data are transferredand is not repeated.

FIG. 6 is a block diagram of an alternative embodiment of a line card126 according to the teachings of the invention. Line card 126 issubstantially similar to line card 26 except that there is notnecessarily a one-to-one correspondence between polling units 142 andassociated physical devices 130. In this example, each polling unitwithin a single line card 126 is associated with a plurality of physicaldevices 130 although there may be a one-to-one correspondence for someof the polling units 142. Select line 146 may comprise a multi-bit linethat allows select unit 40 to transmit the address of the associatedphysical device rather than just a one-bit signal indicating that theassociated device has been selected. Operation of line card 126 issubstantially similar to that of line card 26 except that polling units142 poll all of their associated DSL chipsets 130 until told by selectengine 40 to select a particular one. Once a particular DSL chipset isselected to receive data, polling unit 142 continues to poll all otherunselected DSL chipsets 130 until transfer of data actually occurs.Transfer of data may occur as described above with respect to FIGS. 2through 5.

Although the present invention has been described with several exampleembodiments, various changes in modifications may be suggested to oneskilled in the art. It is intended that the present invention encompassthose changes and modifications as they fall within the scope of theclaims.

1. A method for multicasting data to a plurality of UTOPIA devicescomprising: providing a plurality of UTOPIA physical devices connectedto a common data bus, each UTOPIA physical device operable tocommunicate according to UTOPIA protocol, wherein each UTOPIA physicaldevice is coupled to a respective one of a plurality of polling units,each polling unit coupled to a select controller, the select controlleroperable to initiate selection of two or more of the plurality of UTOPIAphysical devices to receive multicast data; for at least two of thepolling units, receiving at the select controller an indication that therespective UTOPIA physical device is ready to receive data; selectingfor receipt of multicast data two or more of the UTOPIA devices that areready to receive data by: for each UTOPIA physical device to be selectedtransmitting, from the select controller, to the polling unit coupled tothe UTOPIA physical device to be selected, an indication that the UTOPIAphysical device to be selected should be selected; and for each pollingunit receiving an indication that the UTOPIA physical device to beselected should be selected, transmitting an address of the UTOPIAphysical device coupled to the polling unit from the polling unit to theUTOPIA physical device coupled to the polling unit; and after selectionof the two or more of the UTOPIA devices, initiating, by the selectcontroller, transfer of the multicast data through the common bus to theselected UTOPIA physical devices.
 2. The method of claim 1, and furthercomprising receiving, for the at least two of the polling units, fromthe respective UTOPIA physical device, an indication that the respectiveUTOPIA physical device is ready to receive data.
 3. The method of claim1, and further comprising polling, for the at least two of the pollingunits, the respective UTOPIA physical device, to determine if therespective UTOPIA physical device is ready to receive data.
 4. Themethod of claim 3, wherein polling the respective UTOPIA physical devicecomprises transmitting an address of the respective UTOPIA physicaldevice to the respective UTOPIA physical device.
 5. The method of claim1, wherein providing a plurality of UTOPIA physical devices comprisesproviding a plurality of digital subscriber line chipsets.
 6. The methodof claim 1, wherein the plurality of polling units comprises at leasteight polling units and wherein receiving, for at least two of thepolling units, at the select controller an indication that therespective UTOPIA physical device is ready to receive data comprisesreceiving, for at least eight of the polling units, an indication thatthe respective UTOPIA physical device is ready to receive data.
 7. Themethod of claim 1, and further comprising transferring the multicastdata through the common bus to the selected UTOPIA physical devices. 8.The method of claim 1, and further comprising receiving at the selectcontroller an indication of the UTOPIA physical devices for which themulticast data are intended.
 9. A method for multicasting datacomprising: receiving at a line card multicast data and an indication ofa plurality of destinations for the multicast data; transferring themulticast data over a common bus to a plurality of digital subscriberline chipsets associated with the plurality of destinations by:selecting two or more of the plurality of digital subscriber linechipsets to receive multicast data that are ready to receive datawherein the line card comprises one polling unit for each of theplurality of digital subscriber line chipsets, each polling unit todetermine if the associated digital subscriber line chipset is ready toreceive data; enabling the two or more selected digital subscriber linechipsets to receive the multicast data; and transferring the multicastdata over the common bus to the selected digital subscriber linechipsets after selection and enabling of the two or more of theplurality of digital subscriber line chipsets.
 10. The method of claim9, wherein transferring the multicast data over the common bus to theselected digital subscriber line chipsets after selection and enablingof the two or more of the digital subscriber line chipsets comprisestransferring the multicast data over the common bus substantiallysimultaneously to the selected and enabled digital subscriber linechipsets.
 11. The method of claim 9, wherein transferring the multicastdata over a common bus to a plurality of digital subscriber linechipsets after selection and enabling of the two or more of theplurality of digital subscriber line chipsets comprises transferring themulticast data over a common bus to a plurality of digital subscriberline chipsets located on the line card.
 12. The method of claim 9,wherein the line card comprises at least two polling units, each pollingunit coupled to one or more of the digital subscriber line chipsets andoperable to determine if any of the one or more digital subscriber linechipsets is ready to receive data.
 13. The method of claim 9, andfurther comprising receiving at a select controller on the line card anindication that the two or more of the plurality of digital subscriberline chipsets are ready to receive data.
 14. The method of claim 9, andfurther comprising, for each polling unit associated with the two ormore of the plurality of digital subscriber line chipsets, transmittingan indication to a select controller on the line card that the digitalsubscriber line chipset is ready to receive data.
 15. A apparatuscomprising: a buffer; a plurality of UTOPIA physical devices eachcoupled to a common data bus; a plurality of polling units each operableto poll at least a respective one of the UTOPIA physical devices todetermine if the at least one respective UTOPIA physical device is readyto receive data; a select unit to: receive an indication from each ofthe plurality of polling units that a respective UTOPIA physical deviceis ready to receive data; initiate enabling of selected ones of theUTOPIA physical devices that are ready to receive data and for which anydata stored in the buffer is intended such that more than one of theUTOPIA physical devices are enabled to receive data at the same time;and initiate transfer of data stored in the buffer over the common busto the enabled UTOPIA physical devices; and a transfer unit operable totransmit the data stored in the buffer substantially simultaneously tothe enabled UTOPIA physical devices.
 16. The apparatus of claim 15, andfurther comprising, for at least one of the polling units, a pluralityof respective address lines and cell available lines coupling thepolling unit to more than one of the plurality of UTOPIA physicaldevices.
 17. The apparatus of claim 15, and further comprising, for eachpolling unit, an address line and a cell available line coupling thepolling unit to exactly one of the UTOPIA physical devices.
 18. Theapparatus of claim 15, and further comprising, for each polling unit, aselect line and a cell available line coupling the polling unit to theselect unit.
 19. The apparatus of claim 15, and further comprising atransfer unit operable to transfer data from the buffer to the commonbus for receipt by the plurality of UTOPIA physical devices.
 20. Theapparatus of claim 18, wherein the select line comprises a multi-bitselect line.
 21. The apparatus of claim 15, wherein the select unit isfurther operable to initiate enablement of all of the plurality ofUTOPIA physical devices that are ready to receive data and for which anydata stored in the buffer is intended.
 22. The apparatus of claim 15,wherein the buffer, the plurality of UTOPIA physical devices, theplurality of polling units, the select unit, and the transfer unit areformed on a line card.
 23. A line card comprising: a buffer; a pluralityof digital subscriber line chipsets each coupled to a common data bus; aplurality of polling units each operable to poll at least a respectiveone of the UTOPIA physical devices to determine if the at least onerespective UTOPIA physical device is ready to receive data, each pollingunit coupled to at least one of the plurality of UTOPIA physical devicesby an address line and a cell available line; a select unit coupled toeach of the plurality of polling units by respective select lines andcell available lines, the select unit to: receive an indication fromeach of the plurality of polling units that a respective UTOPIA physicaldevice is ready to receive data; initiate enabling of selected ones ofthe UTOPIA physical devices that are ready to receive data and for whichany data stored in the buffer is intended such that more than one of theUTOPIA physical devices are enabled to receive data at the same time;and initiate transfer of data stored in the buffer over the common busto the enabled UTOPIA physical devices; and a transfer unit operable totransmit the data stored in the buffer substantially simultaneously tothe enabled UTOPIA physical devices.
 24. A line card comprising: abuffer; a plurality of digital subscriber line chipsets each coupled toa common data bus; a plurality of polling units each operable to poll atleast a respective one of the UTOPIA physical devices to determine ifthe at least one respective UTOPIA physical device is ready to receivedata, each polling unit coupled a plurality of UTOPIA physical devicesby respective address lines and a cell available lines; a select unitcoupled to each of the plurality of polling units by respective selectlines and cell available lines, the select unit to: receive anindication from each of the plurality of polling units that a respectiveUTOPIA physical device is ready to receive data; initiate enabling ofselected ones of the UTOPIA physical devices that are ready to receivedata and for which any data stored in the buffer is intended such thatmore than one of the UTOPIA physical devices are enabled to receive dataat the same time; and initiate transfer of data stored in the bufferover the common bus to the enabled UTOPIA physical devices; and atransfer unit operable to transmit the data stored in the buffersubstantially simultaneously to the enabled UTOPIA physical devices. 25.The line card of claim 24, wherein the select lines coupling theplurality of polling units to the select unit comprise multiple lines.26. The line card of claim 24, wherein the select lines coupling theplurality of polling units to the select unit comprise a multi-bit line.27. A apparatus comprising: a storage means for temporarily storingdata; a plurality of UTOPIA physical devices each coupled to a commondata bus; a plurality of polling means for polling at least a respectiveone of the UTOPIA physical devices to determine if the at least onerespective UTOPIA physical device is ready to receive data; a selectmeans for: receiving an indication from each of the plurality of pollingmeans that a respective UTOPIA physical device is ready to receive data;initiating enabling of selected ones of the UTOPIA physical devices thatare ready to receive data and for which any data stored in the storagemeans is intended such that more than one of the UTOPIA physical devicesare enabled to receive data at the same time; and initiating transfer ofdata stored in the storage means over the common bus to the enabledUTOPIA physical devices; and a transfer means for transmitting the datastored in the buffer substantially simultaneously to the enabled UTOPIAphysical devices.